A polymer electrolyte fuel cell has been known as one type of fuel cell. Since a polymer electrolyte fuel cell is characterized by low operating temperatures (up to approximately 80° C. to 100° C.), low cost, and its compact size when compared with different types of fuel cells, it is expected to serve as an automobile power source and the like.
As shown in FIG. 4, in a polymer electrolyte fuel cell, a membrane-electrode assembly (MEA) 50, which is used as a main component, is sandwiched by separators 51 each having a fuel (hydrogen) gas channel and an air gas channel such that a single fuel cell 55, referred to as a single cell, is formed. A membrane-electrode assembly 50 has a structure in which an anode-side electrode catalyst layer 53a is laminated on one side of an electrolyte membrane 52 serving as an ion exchange membrane and a cathode-side electrode catalyst layer 53b is laminated on the other side thereof.
A perfluorosulfonic acid polymer thin film (Nafion membrane, DuPont, the U.S.) comprising an electrolyte resin (ion exchange resin) is mainly used as such an electrolyte membrane 52. In addition, since sufficient strength cannot be achieved with the use of a thin film consisting of an electrolyte resin, an electrolyte resin solution may be allowed to impregnate a porous reinforcing membrane (e.g., a thin film prepared by stretching PTFE, polyolefin resin, or the like) such that a reinforced electrolyte membrane is obtained (see Patent Document 1, etc.).
For electrode catalyst layers 53a and 53b, an electrode catalyst material comprising an electrode catalyst such as platinum-supporting carbon and an electrolyte resin is mainly used. A membrane-electrode assembly 50 is obtained by applying such electrode catalyst material to an electrolyte membrane 52 by a screen printing method or the like, followed by drying (see Patent Document 2, etc.).
In view of improvement of power generation performance, it is desirable for a membrane-electrode assembly to have a large effective contact area between an electrolyte membrane and an electrode catalyst layer. In order to achieve such purpose, it has been suggested that a membrane-electrode assembly be obtained by forming recesses and projections on the electrode catalyst layer side in a preliminary step with the use of a press or the like and pressure-welding an electrolyte membrane thereto (see Patent Document 3, etc.).
Patent Document 1: JP Patent Publication (Kokai) No. 9-194609 A (1997)
Patent Document 2: JP Patent Publication (Kokai) No. 9-180728 A (1997)
Patent Document 3: JP Patent Publication (Kokai) No. 2005-293923 A